Abstract

Spectroscopic, spectrophotometric, and photometric data are discussed
which demonstrate that supernova 1975a, located in the NGC 2207/IC 2163
system, was a type I event. January 22.8, 1975, is adopted as the date
of maximum light, and an absolute bolometric magnitude of -19.4 at
maximum light is estimated. The photospheric radius and temperature five
days before maximum light are believed to have been 10 billion km and
12,000 K. The spectroscopic behavior of this supernova is described,
emphasizing observed features that agree well with those seen in other
type I supernovae and several narrow features that might have arisen in
thin shells of absorbing matter. Similar data are discussed for
supernova 1975b, which occurred in an anonymous galaxy of the Perseus
cluster. The wavelengths are shown to agree very well with those
measured for supernova 1975a. The only unusual feature discovered in
1975b was the absence of a clearly defined absorption feature at 6115 A.
It is concluded that 1975b was either a normal type I supernova with the
6115-A feature obscured or a peculiar type I event.

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